Traditional foldable chairs accomplish the folding process by forming a four-bar linkage consisted of front legs, rear legs, a seat frame bar and a connecting member, the rear legs are shorter than the front legs and the top end of the rear leg pivotally connected to the middle-upper portion of the front leg, the middle-rear portion of the seat frame bar pivotally connected to the middle portion of the front leg, one end of said connecting member connected to near rear end of the seat frame bar and the other end of said connecting member pivotally connected to near upper portion of the rear leg. When the foldable chair unfolded completely, said connecting member abut upper to the protrusion disposed on one side of the seat frame bar, thus the seat is fixed to a horizontal position, in this completely unfolded state, said protrusion is below the portion between the two ends of said connecting member, the gravity of the user is mainly in the middle-front portion of the seat, the protrusion ensure that the rear end of the seat frame bar will not be upturned and the middle-front portion will not be droop.
Another folding mechanism of the foldable chair is: the upper end of the front leg pivotally connected to the front end of the horizontal lever, the middle portion of the front leg crossly and pivotally connected to middle-lower portion of the rear leg, the horizontal lever slidably and rotatably connected to the approximately middle portion of the rear leg along the length direction, said horizontal lever used for supporting the seat. When the connecting portion of the rear leg set for connecting the horizontal lever is slide to the utmost front position, the folding mechanism is in folded state, on the contrary, it is in unfolded position.
As to the folding mechanism of the first type, one of the mainly stress-points in the use status is the connecting point between the connecting member and the protrusion of the seat frame bar, therefore, the connecting between the protrusion and the seat frame bar is very important, or else the seat can not be supported stably. As to the mechanism of the second type, the connecting portion between the rear leg and the horizontal bar is one of the mainly stress-points, maintain the stability of the connecting portion is difficult, thus can be seen, the folding mechanism of the prior art are not stable and reliable enough.